1. Field of the Invention
This invention relates to differential disconnect drive assemblies or mechanisms, and in particular to dual disconnect drive assemblies, for four-wheel drive vehicles which can be operated in either a two-wheel drive mode or a four-wheel drive mode.
2. Description of Related Art
Four-wheel drive vehicles, which are operable in either a two-wheel drive mode or a four-wheel drive mode, have gained widespread popularity. Axle disconnect mechanisms, or differential disconnect mechanisms or assemblies for such vehicles are known.
Commonly used disconnect mechanisms for four-wheel drive vehicles disconnect only one of the two output shafts on an axle assembly which is driven part time. This causes the pinion gears and the side gears of the differential to rotate due to back driving, although the differential case remains stationary. This is not compatible with speed-sensitive limited slip differentials. Also, single axle disconnect mechanisms may cause noise and wear and poor fuel economy due to rotation of the differential components while the vehicle is in two-wheel drive mode.
Various dual disconnect differential assemblies or mechanisms have been proposed. These mechanisms in general have an unnecessary number of moving parts, are fairly complex, and would be suitable only for installation on relatively wide vehicles because of the space required. Earlier designs have interposed a clutch member between the side gear and the output shaft. None has achieved desirable commercial acceptance.
This invention comprises a differential having first and second side gears, which are rotatable about a common transverse axis. Rotatable first and second output shafts are co-axial with the side gears and are arranged to drive a pair of respective wheels, and a universal joint (e.g., a constant velocity joint) is disposed between each output shaft and a respective wheel end. In accordance with this invention, a clutch mechanism is used for placing each output shaft simultaneously into or simultaneously out of driving engagement with the inboard side of an associated universal joint. An actuator is used to slidably and concurrently move the output shafts between the clutch engaging position and the clutch disengaging position with respect to the universal joint to thereby disconnect the output shaft from the associated axle shafts and joint assembly.
In the preferred embodiment, the output shafts have clutch members for engaging the clutch members of the respective first and second universal joints, with the output shafts being simultaneously slidable in a first direction to a clutch engaging position and simultaneously slidable in a second direction to a clutch disengaging position. The output shafts are interconnected to provide simultaneous sliding movement.
A preferred dual disconnect differential assembly according to the invention includes, as axially engageable clutch members, a spline interface connection between the first and second universal joints and the respective first and second output shafts. A biasing means is provided for biasing the output shafts to a clutch disengaging position. The vehicle is in two-wheel drive mode when the clutch is disengaged and in four-wheel drive mode when the clutch is engaged. An actuator causes sliding movement of the interconnected output shafts to translate the shafts into the disengaged position.
Another aspect of the clutch mechanism of the invention provides a pair of split-spline teeth on both the output shafts and the respective universal joints to reduce the travel distance required to engage/disengage the dual axle disconnect system.
The differential assembly of the present invention possesses several advantages, including greater fuel economy, less wear, and less noise compared to previously known disconnect mechanism in which only a single output shaft and its axle shaft are disengaged from driving engagement with a differential when two-wheel drive mode is selected. Advantages of the present invention compared to previously known dual disconnect differential assemblies include a more robust design without increased packaged size, fewer parts and greater compactness, which makes it possible to utilize the present dual disconnect drive mechanism on any size vehicle, including a sub-compact automobile. This makes it possible to offer four-wheel drive on smaller vehicles, including sub-compact automobiles, which have not previously had optional four-wheel drive because of the space requirements of presently known dual disconnect mechanism.